Recursive motion for motion detection deinterlacer

ABSTRACT

A recursive motion detector for detecting motion in an interlaced video signal. The motion detector includes a first frame motion detector receiving a next field and a first previous field, a second frame motion detector receiving a current field and a second previous field, and a third frame motion detector receiving a next field and a third previous field. Motion is detected when the first, second and third frame motion detectors combine to produce a frame motion result.

RELATED APPLICATIONS

This application claims the benefit under 35 U.S.C. §120 as acontinuation of U.S. application Ser. No. 12/412,522 titled “RecursiveMotion for Motion Detection Deinterlacer,” filed on Mar. 27, 2009, whichclaims priority under 35 U.S.C. §119(e) to U.S. Provisional ApplicationSer. No. 61/040,027, entitled “Adaptive Windowing in Motion Detector forDeinterlacer,” filed on Mar. 27, 2008, which is herein incorporated byreference in its entirety.

BACKGROUND OF INVENTION

1. Field of Invention

The present invention relates to motion detection used in connectionwith deinterlacing fields of an interlaced video signal.

2. Discussion of Related Art

Video images are displayed on monitors or display screens of varioustypes as a time-sequence of frames shown quickly enough to deceive thehuman eye into perceiving that sequence of frames as a continuouslymoving picture. Each frame consists of a collection of lines of pixels,the precise number of which depend on the technology implemented. Forhistorical reasons, for example reasons which took advantage of oldertechnologies to reduce perceived flicker arising from such anarrangement, each frame was further divided into two fields, each ofwhich contained half of the lines comprising the frame. One fieldcontained every other line of the frame, e.g. the even lines, and theother field contained the lines not included in the first field, e.g.the odd lines. Fields were displayed in even, odd, even, odd, etc.sequence, at twice the frame rate, thus reducing flicker and displayingthe sequence of frames at the frame rate. Such an arrangement of fieldsto form frames is referred to as an interlaced scan display.

Another way of displaying frames is to simply display each line of aframe in sequence, and with such timing as to display frames at thedesired frame rate. Such an arrangement of display is referred to as aprogressive scan display.

When video images are broken down into a sequence of serial elements soas to form a serial signal that can be transmitted from a video imagesource to a video image display, the two-field arrangement isconventionally still used. Therefore, video image display devices thatemploy progressive scan display de-interlace the signal so it can thenbe used to produce entire fields at one time.

In conventional deinterlacer devices, for example, the Supra HD780available from Zoran Corporation, frame motion detection is used asshown in FIG. 1. Conventional frame motion detection compares fields ofthe same polarity, i.e., even-even or odd-odd.

A video image stream 101 is loaded into a buffer 103. At time t-1, framemotion detection is performed by a detector 105 between Field 0 andField 2. A motion value 107 is computed for each corresponding pair ofpixels based on a finite window of pixels around that for which thevalue is being computed. This motion value is then quantized into a2-bit motion value, k, by comparing a quantitative measure of motiondetected to thresholds. This motion value, k, is then written to memory109, which would be read back at time t. Also at time t-1, motion values108 representing motion detected between Field 1 and Field 3 which werepreviously computed and stored in memory 109, or simultaneously computedby detector 111 and stored in memory 109 are read from memory 109.Hence, at time t-1, two motion values are available. Conventionally, oneframe motion detector (frame motion detector 1-3) 111 detects motionbetween field 1 and field 3, while another (frame motion detector 0-2)105 detects motion between field 0 and field 2. (See also FIG. 2). Agoal of this process is to predict the values of pixels in a frame whichare not part of the current field, i.e., the current missing pixels.

Processing by a processor 113, then proceeds as follows: The buffer 103is read out 115 and an output stream 117 either weaved or interpolatedare described. To calculate the final k value for a particular currentmissing pixel, the following is done:

Let k13_top=k value from pixel immediately above the current missingpixel from frame motion detector 13

Let k13_bot=k value from pixel immediately below the current missingpixel from frame motion detector 13

Let k02=k value calculated from frame motion detector 02

if (k13_top > k02 && k13_bot > k02)   k_final = max(k13_top, k13_bot)else   k_final = k02 end.

The current design suffers from motion aliasing, i.e. there isundetected motion. This results in feathering artifacts.

In the Supra HD780, the frame motion detector uses a 3-line by 5-pixelwide window to calculate the Mean Absolute Difference (MAD) as the framemotion value for each pixel.

The MAD of a pixel in missing row i, column j, at time t is calculatedbetween the future and the past fields as follows:

${M\; A\; {D\left( {i,j,t} \right)}} = {\frac{\sum\limits_{k = {- 1}}^{1}\; {\sum\limits_{l = {- 2}}^{2}\; {{{p\left( {{i + k},{j + l},{t + 1}} \right)} - {p\left( {{i + k},{j + l},{t - 1}} \right)}}}}}{16}.}$

The motivation for utilizing a 3×5 window is to suppress the effects ofnoise.

However, because such a big window is used for motion detection, motionthat is far away from the missing pixel will affect the amount of motiondetected at the missing pixel, resulting in the detection of motionwhere there is none.

The MAD values computed by the motion detector are compared to 3programmable thresholds to create a 2-bit ‘k’ value:

$\begin{matrix}{k_{frame} = \left\{ \begin{matrix}{0,{{if}\mspace{14mu} \left( {{M\; A\; D} \leq {{reg\_ frame}{\_ mdetect}{\_ thresh}{\_ a}}} \right)}} \\{1,{{if}\mspace{14mu} \left( {{{M\; A\; D} > {{reg\_ frame}{\_ mdetect}{\_ thresh}{\_ a}}}\&\&{{M\; A\; D} \leq {{reg\_ frame}{\_ mdetect}{\_ thresh}{\_ b}}}} \right)}} \\{2,{{if}\mspace{14mu} \left( {{{M\; A\; D} > {{reg\_ frame}{\_ mdetect}{\_ thresh}{\_ b}}}\&\&{{M\; A\; D} \leq {{reg\_ frame}{\_ mdetect}{\_ thresh}{\_ c}}}} \right)}} \\{3,{{if}\mspace{14mu} \left( {{M\; A\; D} > {{reg\_ frame}{\_ mdetect}{\_ thresh}{\_ c}}} \right)}}\end{matrix} \right.} \\{{{reg\_ frame}{\_ mdetect}{\_ thresh}{\_ a}} \leq {{reg\_ frame}{\_ mdetect}{\_ thresh}{\_ b}} \leq {{reg\_ frame}{\_ mdetect}{\_ thresh}{\_ c}}}\end{matrix}$

This final result from (‘k’ value) is used by the output blender togenerate the missing lines of the output frame, at each field time. Theoutput frame is either weaved from successive odd/even field,interpolated from a single field, or a combination of the two. If motionin the scene is significant, weaving between fields is more likely toproduce a field tearing artifact. A 2-bit ‘k’ motion value allows forfour blending ratios in the output blender. The values currently usedare summarized in the table below:

‘k’ motion value Weave (%) Interpolate (%) 0 100 0 1 50 50 2 25 75 3 0100

The k motion value is quantized into a 2-bit value by comparing toprogrammable thresholds. This quantization creates quantization error.Moreover, 4-level blending creates undesired artifacts in high frequencyimages.

In the Supra HD780, field motion detectors detect motion on two fieldsof opposite polarities, in addition to frame motion detection based onfields of the same polarity. When the frame motion detection and thefield motion detection disagree substantially, a recursive frame motionalgorithm is used to detect motion. A counter is used to keep track ofsituations when the results of the frame motion detector and fieldmotion detector conflict. The counter value is compared to a threshold(moving_threshold below) and used to modify the ‘k’ motion value.

If (k_field > threshhold) // field motion detector detects some motion  If (k_frame == 0) // frame motion detector doesn't detect any motion    historical_motion_counter = historical_motion_counter + 1;   Else    historical_motion_counter = historical_motion_counter − 1; Else    historical_motion_counter = 0.

The historical_motion_counter is saved on the field buffer and read onthe next field.

-   k_curr_fame' is modified as follow:

If (k_field > teething_threshold & historical_motion_counter <moving_threshold)   k_curr_frame′ = k_frame + 1 Else if (k_prev_frame >k_curr_frame)   k_curr_frame′ = k_prev_frame − 1 Else   k_curr_frame′ =k_curr_frame.

-   k_frame is modified as follows:

If (k_field > teething_threshold & historical_motion_counter <moving_threshold)   k_frame′ = k_frame +1 Else   k_frame′ = k_frame.

-   k_frame' can be used as the k motion value.

The recursive motion method embodies in the Supra HD780 requires a 4-bitper pixel field buffer to store the historical counter value, based onusing a 2-bit k motion value. This method still produces artifacts instatic high vertical frequency images, where single-time details arepresent.

SUMMARY OF INVENTION

According to aspects of embodiments, a recursive motion detectorcomprises: a first frame motion detector receiving a next field and afirst previous field; a second frame motion detector receiving a currentfield and a second previous field; and a third frame motion detectorreceiving a next field and a third previous field; wherein motion isdetected when the first, second and third frame motion detectors combineto produce a frame motion result. Variations are possible, including avariation where the motion detector further comprises: a motion detectorcomparator that receives a result from the first frame motion detector,a result for the second frame motion detector and a result from thethird frame motion detector, and produces as the frame motion result, avalue based on the result of the first frame motion detector, whenmotion occurs and on values based on a combination of the result of thesecond frame motion detector and the third frame motion detector, whenhigher speed motion occurs.

According to aspects of another embodiment, a method of detecting framemotion comprises: defining frame motion values frame_curr andframe_final according to:

if (frame04 > frame02)   frame_curr = max(frame02, frame04/2); else  frame_curr = frame02; end if (frame13_top > frame_curr &&frame13_bot > frame_curr)   frame_final = min(frame13_top, frame13_bot);else   frame_final = frame_curr; end.This method may further comprise: defining a blend ratio blend, definingweighting between assigning values to a line using either weaving orinterpolation, according to:

  topbot_diff1 = abs((next_top + prev_top)/2 − (next_mid +prev_mid)/2));   topbot_diff2 = abs((next_bot + prev_bot)/2 −(next_mid + prev_mid)/2));   topbot_diff = max([topbot_diff1topbot_diff2]) − topbot_thresh; blend = topbot_diff + blend_res/2; if(blend<0)   blend = 0; elseif (blend > blend_res)   blend = blend_res;end.This method may yet further comprise: selecting between a recursive modeand a frame motion mode according to:

If (recursive_motion_mode)   If (frame_motion > field_motion)    blend_factor = frame_motion     motion_writeback = frame_motion    recursive_motion = 0   else if (prev_motion >= field_motion)    blend_factor = frame_motion     motion_writeback = prev_motion +field_motion /     steps −     frame_motion     recursive_motion = 1  else     blend_factor = blend of field_motion and     frame_motion    motion_writeback = prev_motion + field_motion /     steps −    frame_motion     recursive_motion = 1   end else   if(field_motion > frame_motion)     blend_factor = field_motion    motion_writeback = field_motion     recursive_motion = 1   else    blend_factor = frame_motion     motion_writeback = frame_motion    recursive_motion = 0   end end,

where motion_writeback is written to memory and subsequently read backin the next frame as frame13_top and frame13_bot (see above), resultingin recursion.

BRIEF DESCRIPTION OF DRAWINGS

The accompanying drawings are not intended to be drawn to scale. In thedrawings, each identical or nearly identical component that isillustrated in various figures is represented by a like numeral. Forpurposes of clarity, not every component may be labeled in everydrawing. In the drawings:

FIG. 1 is a block diagram of a prior art system for frame motiondetection;

FIG. 2 is a representation of frame memory contents compared using theprior art system;

FIG. 3A is an overview block diagram of aspects of an embodiment;

FIG. 3B is a lower-level block diagram of aspects of an embodiment;

FIG. 4 is a representation of frame memory contents compared using thesystem;

FIG. 5 is a flow diagram of a method according to an embodiment ofaspects of the invention;

FIG. 6 is a graph of the blending function; and

FIG. 7 is a flow diagram of a recursion method according to anembodiment of aspects of the invention.

DETAILED DESCRIPTION

This invention is not limited in its application to the details ofconstruction and the arrangement of components set forth in thefollowing description or illustrated in the drawings. The invention iscapable of other embodiments and of being practiced or of being carriedout in various ways. Also, the phraseology and terminology used hereinis for the purpose of description and should not be regarded aslimiting. The use of “including,” “comprising,” or “having,”“containing”, “involving”, and variations thereof herein, is meant toencompass the items listed thereafter and equivalents thereof as well asadditional items. The invention is illustrated by the followingdescription of aspects of embodiments thereof. Some aspects andembodiments relate to different parts of a larger aspect or embodiment,and represent alternatives that may be combined variously to formvariations on a larger embodiment.

The exemplary aspects and embodiments relate to deinterlacers used inhigh definition television (HDTV) displays, although other applicationswill occur to the skilled artisan.

A high-level overview of the system according to aspects of someembodiments is shown in FIG. 3A. The elements shown may be implementedas software executing on a suitable general purpose processor, specialpurpose image processor, digital signal processor (DSP), or the like, oras specialized hardware implementing the various functions in logic, oras a combination of these. In some implementations, where a function iscalled for to process different input values, only one instance of thefunction may be incorporated into the implementation, and reused atdifferent points in time, or, alternatively, multiple instances of thefunction may be incorporated into the implementation, and the multipleinstances used in parallel.

The system includes a memory, 321, in which input buffers, outputbuffers, temporary storage registers and the like are defined to holdvarious values, such as the values comprising the serial elements of theserial signal. Connected to the memory, 321, are four frame motiondetectors, 323 a, 323 b, 323 c and 323 d, two of which detect motionbetween fields 0 and 2, 323 a and 323 b, and two of which detect motionbetween fields 0 and 4, 323 c and 323 d. Two of the frame motiondetectors, 323 a and 323 c, employ a three-line by five-pixel window,while the other two frame motion detectors, 323 b and 323 d, employ aone-line by five pixel window. The results of frame motion detection arepair-wise inputs to selective blending, 325 a and 325 b, to producemotion values corresponding to one-frame, frame02, and two-frame,frame04, intervals. The blended results corresponding to one-frame,frame02, and two-frame, frame04, intervals are further processed, 327and 329, as described in connection with FIG. 5, below.

A field motion detector, 331, receives frames 0, 1 and 2, and produces afield motion result. Frame and field motion results are used by arecursive motion module, 333, to determine whether recursive motiondetection is required by the nature of the serial signal. Finally, theblend factor computed by selective blending, 325 a and 325 b, is appliedto a weaver/interpolator, 335, which employs a degree of weaving and aninverse degree of interpolating determined by the blend factor to createpredicted pixels in an output field.

The operation of the system whose overview has been presented inconnection with FIG. 3A is now described in connection with FIGS. 3B, 4,5, 6 and 7.

According to aspects of embodiments shown in FIG. 3B, a serial signal101 representing in digital form an interlaced video signal is receivedinto a buffer memory 301. A processor, which may be special-purposeprocessor, or a general-purpose processor, or a digital-signal processorreads the signal from the buffer memory, performs various method stepsand writes a result to a buffer memory or other output. The methodincludes frame motion detection, windowing and recursive frame motiondetection as described below.

Basic Motion Detection

According to aspects of an embodiment, frame motion detection is donebetween three pairs of fields. Frame motion detection is done betweenfields 0 and 2 by detector 303 and fields 1 and 3, by detector 305 aswell as between fields 0 and 4 by detector 307. This improves theoverall frame motion detector's ability to detect motion over that ofconventional detectors, hence reducing feathering artifacts. (See alsoFIG. 4).

Detector results are stored in memory 309, after which they areprocessed by processor 311 then produces an output stream 313 from theseries of fields 315 read from buffer 301. In accordance with the methodaccording to aspects of an embodiment, as shown in FIG. 5, to calculatethe final motion value, the following is done:

Let frame13 _top=frame motion value from pixel immediately above thecurrent missing pixel from frame motion detector 13

Let frame13_bot=frame motion value from pixel immediately below thecurrent missing pixel from frame motion detector 13

Let frame02=frame motion value calculated from frame motion detector 02

Let frame04=frame motion value calculated from frame motion detector 04

With three motion detector values available, (FIG. 5, 501, 503, 505) thecurrent frame motion value is determined as follows. The order in whichthe three values are obtained does not matter.

if (frame04 > frame02) (FIG. 5, 507)   frame_curr = max(frame02,frame04/2); (FIG. 5, 509) else   frame_curr = frame02; (FIG. 5, 511)end.

When an object is moving within the 5-field window, the motion value offrame04 will be about twice that of frame02, and so the maximum ofeither frame02 or frame04/2 is used, 509. However, when the object isfast moving (i.e. it moves beyond the 5-field window), the motion valuesof frame04 and frame02 will be the same. The pseudocode above providesthat the value of frame02 is then used, 511.

With this new current frame motion value, the same conditions apply asbefore, to calculate the final motion value:

  if (frame13_top > frame_curr && frame13_bot > frame_curr) (FIG. 5,513)     frame_final = min(frame13_top, frame13_bot); (FIG.5 515)   else    frame_final = frame_curr; (FIG. 5, 517)   end.

In contrast with conventional systems, aspects of an embodiment use theminimum value of frame13_top and frame13_bot, 515, instead of using themaximum. According to this aspect, the most accurate motion value iscomputed, instead of biasing the value to the maximum.

Biasing the value to the maximum was conventionally thought to besuperior because doing so forced interpolation to be performed moreoften in instances where the determination of motion remained uncertain,thus avoiding feathering artifacts that would result from improperlyblending when interpolation should be called for. The conventionalapproach is based on an assumption that the motion detector cannotdetect all motion, and therefore should be biased towards detecting moremotion. This approach also, however, increases flickering or reduceddetail artifacts by interpolating excessively, when blending should havebeen done instead.

Using the most accurate motion value as described above has now beenfound to be superior, particularly in connection with the describedaspects of embodiments because these aspects of embodiments detect moreof the motion actually present, thus increasing, without an artificesuch as biasing, the number of instances in which the motion detectordetects motion actually present and therefore indicates interpolationshould be performed rather than blending. By better matching the use ofinterpolation and blending to the actual presence or absence of motionin an image, feathering, flickering and reduced detail artifacts are allavoided.

Interpolation and Blending

Interpolation or blending is performed as indicated after performing aMean Absolute Difference (MAD) computation on a rectangular window ofpixels as follows. The windows may be 3×5 or 1×5 as now described.

An error that can occur is called ‘false interpolation’. Falseinterpolation occurs when interpolating is performed on pixels for whichit should not be done. False interpolation occurs due to detection ofmotion where none is present, and is most visible on objects withhorizontal edge (e.g. a horizontal line). It is not desirable to use aMAD 3×5 window at the edges of a moving horizontal line since falsemotion will be detected and false interpolation will result, creatingvisibly obvious artifacts. When a horizontal line appears in such a 3×5window, away from the pixel under consideration at the center of thewindow, the horizontal line may appear to signify motion at the pixelunder consideration, similarly to noise as described in connection withconventional systems.

Hence, a 1×5 window should be used at horizontal edges to determine themotion value. Of course, the choice of the precise size of the twowindows is left to the skilled artisan, with one window having multiplelines and a multiple pixel width, while the other window is verticallynarrower to avoid noise and horizontal line artifacts.

The results of 3×5 window MAD and 1×5 window MAD are blended based onthe difference between the top/mid lines and mid/bottom lines in thenext and previous fields:

  topbot_diff1 = abs((next_top + prev_top)/2 − (next_mid +prev_mid)/2));   topbot_diff2 = abs((next_bot + prev_bot)/2 −(next_mid + prev_mid)/2));   topbot_diff = max([topbot_diff1topbot_diff2]) − topbot_thresh; blend = topbot_diff + blend_res/2; if(blend<0)   blend = 0; elseif (blend>blend_res)   blend = blend_res;end;where topbot_thresh, blend_res are programmable registers;

-   topbot_thresh signifies the difference between pixel values that can    represent different objects in a picture;-   blend is the blend factor; and-   blend_res is the blending resolution.

To make the 1×5 window MAD value comparable to the 3×5 window MAD, the1×5 MAD, the sums of absolute differences for the detector and window(e.g., sad02_win1×5 and sad02_win3×5, for frame02) must be multiplied by3 before being divided by 16 so they can be blended, as follows.

frame02=round(((sad02_win1×5)*3/16*blend)+((sad02_win3×5)/16*(blend_res-blend)))/blend_res.

This blending operation is done on all frame motion detectors in thedeinterlacer. (i.e. including frame04)

In the new design, a 16-step blending value is used. MAD value isnormalized as follows:

mad_curr_cored=round((mad_curr-mad_core_thresh)* mad_core_normalize);

where mad_core_thresh and mad_core_normalize are programmable registers,and mad_curr_cored is made to saturate at a value of 16. Forcingmad_curr_cored to saturate at 16 may be done by any suitable means. Thefollowing illustrates the transfer function of the blend factor:

This blend factor is used to blend between the interpolated line and theweaved line. The higher the blend factor (i.e. the higher the MADvalue), the more weight is given to the interpolated line. (See FIG. 6).

It is desired to have a 0 response for low MAD values to mask out noise.Hence, for one or more values of MAD near or at 0, the blend factor isforced to saturate at a value of 0 at the low end.

Recursion

The system performs a recursive computation under specified conditions,as shown in FIG. 7. This is called recursive motion mode. In order toperform the method shown in FIG. 7, in addition to basic motiondetection as described above, the system includes two field detectors(FIGS. 3B, 317 and 319), whose outputs are stored and processed (FIGS.3B, 309 and 311) to provide a field motion result which is used togetherwith the frame motion result as described now. The results of theindividual field motion detectors (FIGS. 3B, 317 and 319) are combined,either algebraically or logically to form the field motion result. Anysuitable function can be used to form the combination, such as takingthe maximum of the outputs of the two field motion detectors (FIGS. 3B,317 and 319). The field motion detectors are shown in FIG. 3B asseparate elements within the overall motion detector structure; however,skilled artisans will recognize that the detectors, memory and processorshown may share or reuse elements, or may be constructed usingindependent elements, as various implementations may require forpurposes of speed or economy of hardware.

The system compares, at 701, the field motion detector result 703 withthe frame motion detector result 705. If the field result 703 is greaterthan the frame result 705, the system enters into 707 recursive motionmode 709.

While in the recursive motion mode 709, the field result 703, divided,at 711, by a programmable number of steps 713, is written back, at 715,to a memory location or register used as an accumulator. Once theaccumulator value becomes greater, at 717, than the current field motiondetector result 719, the image is considered to be static, at 721—andweaving, 723 is done. Otherwise, at 721, while inside the recursivemotion mode 709, the field motion detector result 703 is used as theblend factor to the final blender 725.

Recursive motion mode ends, at 727, when the frame motion detectorresult is greater than the field motion detector result.

The following is the simplified pseudo code for the logic.

If (recursive_motion_mode)   If (frame_motion > field_motion)    blend_factor = frame_motion     motion_writeback = frame_motion    recursive_motion = 0   else if (prev_motion >= field_motion)    blend_factor = frame_motion     motion_writeback = prev_motion +field_motion /     steps − frame_motion     recursive_motion = 1   else    blend_factor = blend of field_motion and     frame_motion    motion_writeback = prev_motion + field_motion /     steps −frame_motion     recursive_motion = 1   end else   if (field_motion >frame_motion)     blend_factor = field_motion     motion_writeback =field_motion     recursive_motion = 1   else     blend_factor =frame_motion     motion_writeback = frame_motion     recursive_motion =0   end end;

where steps is a programmable register (power of 2) defining the numberof steps that the deinterlacer will go into weave mode.

recursive_motion is a one-bit indicator that is written back to memory.

recursive_motion_mode is on if either the previous top or previousbottom line of data has recursive_motion_mode on.

prev_motion is the motion data in memory. If both previous top andprevious bottom recursive_motion_mode are on, the maximum of the top andbottom motion data is used. Otherwise, the corresponding motion readback data is used.

The motion detector described can be applied to the luminance or chromacomponents of an image signal, or to both, in accordance with variousembodiments.

When film is converted to video, various artifacts peculiar to thatprocess must be taken into account. They are related to the differencein frame rates and the accuracy with which physical film frames arealigned with those digitized counterparts. Therefore, a film detectionmode is used. In film detection mode, a dedicated k motion value is usedto detect cadences, i.e., those variations that may be film conversionartifacts. This k motion value will also be determined by using the 3×5MAD window, in an exemplary embodiment.

Due to bandwidth constraints, an extra field of memory read may not bepossible in certain usage scenarios. Therefore, there will be an optionto use a 3-field deinterlacer instead of 5.

Since embodiments described above perform 3 field reads from memory,bandwidth to accomplish cadence detection over an entire image becomes amajor concern. One approach to reduce memory bandwidth is to downsamplea field before writing to memory and upsample when reading back.According to an exemplary embodiment, this would be done for field4only. Even though this requires an extra memory write client, the memoryread and memory write sizes can be significantly reduced, hence reducingboth memory footprint and memory bandwidth.

The film mode detector mentioned above is, of course, designed fordetecting cadences that occur on the entire image. This solution is bestsuited for use when a film source fills each image frame entirely,however, for overlayed video, where the video from different sourceshave different cadence sequences, the film mode detector will fail. Oneway to address this issue is to limit cadence detection to predeterminedor other limited regions, including those as small as a single pixel.

Having thus described several aspects of at least one embodiment of thisinvention, it is to be appreciated various alterations, modifications,and improvements will readily occur to those skilled in the art. Suchalterations, modifications, and improvements are intended to be part ofthis disclosure, and are intended to be within the spirit and scope ofthe invention. Accordingly, the foregoing description and drawings areby way of example only.

What is claimed is:
 1. A motion detector for detecting motion in aninterlaced video signal, the motion detector comprising: a frame motiondetector receiving a first field of the interlaced video signal and asecond field of the interlaced video signal, the first field beingdifferent from the second field and having a same parity as the secondfield, the frame motion detector being configured to determine a firstmotion value based on the first field and the second field by using afirst window having a first size, to determine a second motion valuebased on the first field and the second field by using a second windowhaving a second size, the second size being different from the firstsize, and to selectively blend the first motion value and the secondmotion value to generate a frame motion value corresponding to a missingpixel of a current field of the interlaced video signal; and a fieldmotion detector receiving the current field and a third field of theinterlaced video signal, the third field having an opposite parity tothe current field, the field motion detector being configured togenerate a field motion value corresponding to the missing pixel basedon the current field and the third field.
 2. The motion detector ofclaim 1, wherein the frame motion detector is a first frame motiondetector and the frame motion value is a first frame motion value, themotion detector further comprising: a second frame motion detectorreceiving a plurality of input fields of the interlaced video signal,the plurality of input fields having a same parity, the second framemotion detector being configured to generate a second frame motion valuecorresponding to the missing pixel of the current field; and a framemotion detector comparator that receives the first frame motion valueand the second frame motion value and produces a resultant frame motionvalue based on the first frame motion value and the second frame motionvalue.
 3. The motion detector of claim 2, wherein the second framemotion detector is further configured to: determine a respective firstmotion value based on the plurality of input fields by using arespective first window having the first size; determine a respectivesecond motion value based on the plurality of input fields by using arespective second window having the second size; and selectively blendthe respective first motion value and the respective second motion valueto generate the second frame motion value.
 4. The motion detector ofclaim 1, further comprising: a recursive motion detector configured toreceive the frame motion value and the field motion value and togenerate a motion value corresponding to the missing pixel.
 5. Themotion detector of claim 4, wherein the recursive motion detector isfurther configured to: compare the frame motion value to the fieldmotion value; and output the frame motion value as the motion valuecorresponding to the missing pixel in response to determining that theframe motion value is greater than or equal to the field motion value.6. A method of detecting motion in an interlaced video signal, themethod comprising: generating a frame motion value corresponding to amissing pixel of a current field based on a first field of theinterlaced video signal and a second field of the interlaced videosignal, the first field being different from the second field and havinga same parity as the second field; and generating a field motion valuecorresponding to the missing pixel based on the current field of theinterlaced video signal and a third field of the interlaced videosignal, the third field having an opposite parity to the current field;wherein generating the frame motion value includes determining a firstmotion value based on the first field and the second field by using afirst window having a first size, determining a second motion valuebased on the first field and the second field by using a second windowhaving a second size, the second size being different from the firstsize, and selectively blending the first motion value and the secondmotion value to generate the frame motion value.
 7. The method of claim6, wherein the frame motion value is a first frame motion value, themethod further comprising: generating a second frame motion valuecorresponding to the missing pixel based on a plurality of input fieldshaving a same parity; and comparing the first frame motion value and thesecond frame motion value to produce a resultant frame motion valuebased on the first frame motion value and the second frame motion value.8. The method of claim 7, wherein generating the second frame motionvalue includes: determining a respective first motion value based on theplurality of input fields by using a respective first window having thefirst size; determining a respective second motion value based on theplurality of input fields by using a respective second window having thesecond size; and selectively blending the respective first motion valueand the respective second motion value to generate the second framemotion value.
 9. The method of claim 6, further comprising: generating amotion value corresponding to the missing pixel in response togenerating the frame motion value and the field motion value.
 10. Themethod of claim 9, wherein generating a motion value includes: comparingthe frame motion value to the field motion value; and outputting theframe motion value as the motion value in response to determining thatthe frame motion value is greater than or equal to the field motionvalue.